Background: In the Phase II Study 19 trial (NCT00753545; Ledermann et al. Lancet Oncol 2014), maintenance olaparib improved progression-free survival (PFS) vs placebo in PSR OC pts, including those in the non-BRCAm subgroup. A significant PFS benefit was also seen with maintenance olaparib vs placebo in gBRCAm PSR OC pts in the Phase III SOLO2 trial (NCT01874353; Pujade-Lauraine et al. Lancet Oncol 2017). To investigate olaparib maintenance monotherapy in non-gBRCAm PSR OC pts who had received ≥2 previous lines of platinum-based chemotherapy, we performed the Phase IIIb, single-arm, OPINION study (NCT03402841). Methods: Pts had high-grade serous or endometrioid OC and had responded to platinum-based chemotherapy. Pts initiated maintenance olaparib tablets (300 mg bid) until disease progression or unacceptable toxicity. Primary endpoint was investigator-assessed PFS (modified RECIST 1.1). Secondary endpoints included PFS by homologous recombination repair deficiency (HRD; assessed with the Myriad myChoice HRD plus test; HRD+ve: score ≥42) and somatic BRCA mutation (sBRCAm) status. An interim analysis was planned after ~135 PFS events. Results: 279 pts were enrolled from 17 countries (mean age: 64 yrs); 94.3% were confirmed non-gBRCAm by local testing. At data cut-off (Nov 15, 2019), the median PFS was 9.2 months (95% confidence interval [CI]: 7.6–10.9 months), with 152 PFS events (54.5% maturity). The Table presents PFS outcomes by key subgroups. The median exposure to olaparib was 8.1 months. Grade ≥3 adverse events (AEs) occurred in 72 (26%) pts. 19% of pts reported serious AEs. No deaths related to AEs were reported. AEs led to dose interruption, dose reduction and treatment discontinuation in 39%, 15% and 7% of pts, respectively. Conclusions: Maintenance olaparib demonstrated activity in non-gBRCAm PSR OC pts. There were no new safety signals. Clinical trial information: NCT03402841

CR, complete response; NE, not evaluable; NED, no evidence of disease; PR, partial response